Liquid fuels, such as diesel fuel, are used in internal combustion engines of various configurations and sizes. Such fuels must generally be filtered so as to remove particulate contaminants, which can otherwise create significant problems in engine performance and can result in damage to the engine. Filter media for removal of these particulate contaminants has generally been required to remove very high percentages of particles, necessitating use of filter media with tight pore structures. Without such tight pore structures, unacceptable levels of particles can pass through the filter media and detrimentally affect engine performance.
One media currently used for removal of particulate contaminants from fuel streams is melt-blown media that allows for effective removal of particulate contaminants. Although melt-blown media can perform adequately in removing particulate contaminants from liquid fuels, the melt-blown media can readily foul from buildup of contaminants other than traditional particulate contaminants. This premature fouling appears to be particularly pronounced in situations where fuel undergoes repeated heating and cooling cycles, such as in common rail systems used on many diesel engines. In such systems diesel fuel is pumped from a fuel tank at high pressure along a common conduit (or rail) that is connected to multiple fuel injectors. Some of the diesel fuel passes through the fuel injectors and is combusted, but the remainder is delivered back to the fuel tank at an increased temperature as a result of travelling down the common rail through portions of the hot diesel engine. Once back in the tank the fuel rapidly cools. Repeated cycles of heating and cooling of the fuel are believed to contribute in the production of fuel degradation products that accelerate fouling of traditional fuel filter media.
In addition to filter-clogging materials generated as a result of heating and cooling cycles, additional sources of contaminants that can reduce fuel filter performance include ingredients found in various biodiesel mixtures. Although often distinct in origin from the fuel degradation products formed during heating and cooling cycles, these contaminants can also contribute to significant reductions in fuel filter life by accumulating on the filter media. Finally, even normal aging of fuel, especially when it occurs at heightened temperatures, can result in production of fuel contaminants that further limit fuel filter life due to fouling and clogging of filter media earlier than would otherwise be expected if only hard particle contaminants were present.
Therefore, a substantial need exists for filtration media, filter elements, and filtration methods that can be used for removing contaminant materials from liquid fuel streams. The invention provides such media, filter elements and methods.